Functor Fact

The microcosm principle ncatlab.org/nlab/show/micr…

Why is an empty sum 0 and an empty product 1? johndcook.com/blog/2015/04/1…

Kan's paper introducing adjoint functors ams.org/journals/tran/… [pdf]

Introduction to Categories and Categorical Logic arxiv.org/abs/1102.1313v1

A groupoid is a category in which every morphism is an isomorphism.

diagrams: a vector graphics DSL built on Haskell projects.haskell.org/diagrams/

System F is a typed lambda calculus that forms the theoretical basis for ML and Haskell. en.wikipedia.org/wiki/System_F

Computational trinitarianism ncatlab.org/nlab/show/comp…

"The concept of adjoint functor is ... is a strictly category-theoretical notion that has turned out to be a conceptual tool of the first magnitude -- on par with the idea of a continuous function." -- Steve Awodey

Test functions, test charges, and test objects johndcook.com/blog/2023/10/0…

'Adjoint functors arise everywhere.' -- Saunders Mac Lane

'Sometimes, the elegant implementation is a function. Not a method. Not a class. Not a framework. Just a function.' -- John Carmack

In #Haskell, the same name cannot be used for a type constructor and type class in the same scope.

Primitive recursive functions johndcook.com/blog/2016/08/2…

Category theory, like dimensional analysis, can find errors by providing a sanity check for models.

Pragmatic functional programming by @unclebobmartin blog.cleancoder.com/uncle-bob/2017…

A terminal object is a the limit of the empty diagram. An initial object is a colimit of the empty diagram.

Seven dogmas of category theory johndcook.com/blog/2013/06/0…

Typeclassopedia wiki.haskell.org/Typeclassopedia

Category theory for the sciences math.mit.edu/~dspivak/